Towing a trailer often places a significant drag on the towing vehicle which could result in diminishing the power available for other needed functions such as steering and climbing steep hills as well as result in decreased fuel efficiency. Likewise, for a bicycle towing a trailer, the load exerted by the trailer may exhaust a bicyclist climbing a steep hill which could compromise his or her ability to safely steer the bicycle. This problem is most acute for electric cars or hybrid electric vehicles towing a heavy trailer as they are more power limited than combustion engine vehicles. Another serious issue that may be encountered is an uncontrollable yawing of the trailer from side to side potentially resulting in jackknifing of the trailer.
A variety of solutions are offered in prior art references for controlling various aspects of towing a vehicle. U.S. Pat. No. 4,023,864 discloses an automatic stability control system which senses the lateral acceleration of a vehicle by way of strain gauge sensors, or the like, to provide lateral acceleration signals to an amplifier. U.S. Pat. No. 4,269,280 is for a propulsion apparatus including a prime mover and a secondary, or auxiliary, mover, which is controlled so as to achieve efficient use of energy resources. For battery powered prime movers, the disclosed invention causes the battery to be discharged in the more efficient, low current drain manner as much as possible. To accomplish this objective, the control signal to the secondary mover can be such that, for low current drains, the prime mover battery supplies all of the power but that above a certain predetermined threshold current drain from the battery, the secondary mover begins supplying power in such amounts as to reduce the current utilization of the prime mover to the predetermined threshold level. U.S. Pat. No. 5,988,000 relates to a system and method for measuring the strain forces on a load bearing member having a top surface, a bottom surface, a right surface and a left surface. U.S. Pat. No. 6,516,925 discloses a system for use on a trailer. The system includes a motor controller, a pair of electric motor/generators, a battery, a battery controller, and sensors. The battery controller monitors the yaw rate of trailer. Based upon the monitored yaw rate, the controller selectively activates the motor/generators which provide a regenerative braking torque to the axle assembly thereby applying braking force to the trailer and generating electrical energy which may be used to recharge battery. U.S. Pat. No. 6,705,684 describes a tow ball mounted to a bracket by means of a spacer which incorporates transducers to provide signals indicating forces existing between the towing vehicle and the trailer. A control system is described which is operable to apply braking to the trailer to modify the trailer behavior independently of operation of the vehicle brakes by the operator. U.S. Pat. No. 6,725,955 refers to a two wheeled trailer is used to propel a two wheeled vehicle such as a bicycle or a scooter. The trailer is powered by an electric motor and at least one battery. The control of the motor is through a potentiometer attached to the handlebars of the vehicle and in electrical communication with a controller. The trailer is attached to the vehicle by an attachment arm that is mounted near the rear axle of the vehicle. A coupler that allows three axes of rotation attaches the trailer to the vehicle. U.S. Pat. No. 4,199,037 teaches an electrically-powered vehicle which includes an automobile body and frame that carries an electric motor, a battery and a removable trailer which carries a combustion engine and a generator and which is towed by the automobile body and frame. The vehicle can be operated with the trailer member attached and the motor powered by the parallel combination of the battery and generator, or, alternatively, with the trailer member removed and the motor powered for limited distances by the battery alone. U.S. Pat. No. 6,390,215 provides for an electric vehicle that includes a main battery mounted on a vehicle body and a sub-battery detachably connected to the vehicle body. The electric vehicle travels with the electric power of the main battery in the case where the traveling distance is not long. In the case where the traveling distance is long, a trailer with the sub-battery is coupled to the rear of the electric vehicle, so that both the electric powers of the two batteries are used to drive an electric motor to allow the electric vehicle to travel. U.S. Pat. No. 7,147,070 discloses an improved tractor trailer having a tractor unit and a trailer unit in which the tractor unit includes an internal combustion engine. The improvement comprises an electrical drive arranged to drive at least some of the wheels on at least one of the axles of the trailer, in a control system associated therewith. The arrangement provides extra power for situations where it is required and can, in the case of electric drive motors mounted directly on the wheel, provide for better braking. US Pre-grant publication number 20080023234 relates to a two-wheeled trailer attached to a human powered vehicle such as a bicycle or a scooter for carrying load such as children. The trailer is powered by two electric motors and at least one battery. The control of the motor is through a force/pressure meter inserted to the attachment arm between the two wheel vehicle and the trailer. The attachment arm, on the vehicle side is mounted near the rear axle of the vehicle. A coupler that allows free rotation attaches the trailer to the vehicle.
As can be seen, the prior art does not generally deal with controlling and optimizing the performance of a vehicle towing a trailer as it relates to such criteria as providing power when needed, maintaining a constant towing load, fuel efficiency and the issue of trailer swaying from side to side.